The Food and Drug Administration says a study of 700-heart disease patients taking Chantix showed a small uptick in heart problems among those taking the smoking-cessation drug versus those taking placebo. The agency stressed that the drug helped patients quit smoking and that this benefit should be weighed against any potential heart risks.

The FDA will add new warnings to the drug's label about the study's findings. Drugmaker Pfizer will be required to analyze a large group of studies to further define the heart risk.

New York-based Pfizer Inc. reported sales of $755 million for Chantix last year.